The AT&T public switched network employs a centralized database (NCP) to translate a telephone number of a so-called 800 or 900 service call into an associated destination code. It can be appreciated that a centralized database could be driven into an overload condition if it receives from a switching office and within a short duration of time a large number of translation requests directed to a particular 800 or 900 service telephone number. To handle this problem, the centralized database employs a conventional rate-based call control strategy to track the rate of such requests. If the database finds that the rate of such requests meets a predetermined limit, then the database reduces the rate by causing the switching office to block, for a limited duration, subsequent calls directed to the particular service number.
For example, if the established rate is two requests per second, then the database accepts from a particular switching office and for a particular service telephone number a maximum of two requests within a one-second interval, in which the interval is equally divided among the number of requests and begun upon receipt of the first of such requests. Accordingly, the database would respond to the first request and begin the one-second interval. However, if the database receives a second request within the first-half of the one-second interval, then the database would block that request. It can be appreciated that if the database did not receive over the remainder of interval a request associated with the particular service telephone number, then the associated rate for that telephone number would be reduced to one request for the current interval.
Included in the family of 800 and 900 services is a so-called high-capacity (HICAP) service, which is provided to handle a large volume of calls that may be received in response to a particular national (or regional) mass call-in promotion. A characteristic of HICAP calls is that a majority of the calls are typically placed during a short duration of time, usually during the first several minutes of the promotion. As such, the rate of translation requests that the data base would receive from a particular switching office would quickly exceed the established rate, thereby causing the database to impose blocking. However, such blocking would undermine the success of a HICAP promotion, which depends on an appreciable number of calls reaching the destination defined by the associated promotion telephone number.
Herein lies the nub of the problem. On the one hand, an appreciable number of calls need to reach the HICAP destination to ensure that the promotion would enjoy a certain measure of success. On the other hand, if the allowed number of HICAP translations requests all occur within the same segment of the interval, then the database in accord with the rate-based strategy would impose blocking, thereby restricting the number of calls that would reach the promotion number, and thereby undermining the success of the HICAP promotion.